Pressureless sintered silicon carbide ceramic special-shaped beam and preparation method thereof

Abstract

The invention relates to the technical field of preparation of silicon carbide ceramic special-shaped beams, in particular to a pressureless sintered silicon carbide ceramic special-shaped beam and a preparation method thereof.The pressureless sintered silicon carbide ceramic special-shaped beam comprises the following components and structures: material composition: a base material is silicon carbide powder, the particle size is in bimodal distribution, a main phase is 3-5 microns, and a nanophase is 0.5-1 micron; a composite sintering aid; through innovative design of material composition and structure, multi-scale synergistic reinforcement and surface gradient protection are realized, bimodal distributed silicon carbide powder is adopted as a matrix, and through the synergistic effect of a micron-sized particle skeleton and nano-particle filling pores, internal cracks caused by uneven shrinkage of a special-shaped section are remarkably reduced, so that the surface gradient protection performance is improved. And meanwhile, the composite sintering aid can inhibit abnormal growth of crystal grains, synergistically reduce the sintering temperature and reduce the deformation risk of the multi-cavity structure, the crack propagation resistance of the corner angle is greatly improved through the gradient reinforcement phase, and the problem that a hardened layer at the special-shaped corner angle is not uniform is solved through deep siliconizing reinforcement.

Description

Technical Field

[0001] The invention relates to the technical field of preparing silicon carbide ceramic special-shaped beams, and in particular to a pressureless sintered silicon carbide ceramic special-shaped beam and a preparation method thereof. Background Art

[0002] Pressureless-sintered silicon carbide ceramic shaped beams are load-bearing structural components with non-rectangular cross-sections, manufactured using a pressureless sintering process. These beams are core load-bearing components for high-end industrial furnaces and high-temperature equipment. Their structural stability, long lifespan, and energy-saving properties in extreme environments make them a leading alternative to metals and conventional ceramics, making them particularly valuable in applications requiring customized cross-sectional designs.

[0003] For example, a pressureless liquid phase sintered silicon carbide ceramic and its preparation method with application number CN202310133308.2 and authorization announcement date 20230620. The silicon carbide ceramic is obtained by sequentially heating degumming and pressureless liquid phase sintering of a blank, and the blank is pressed from granulated powder, and the granulated powder is obtained from slurry through centrifugal spray granulation. The components of the slurry include deionized water. In addition to deionized water, the slurry also includes the following components in parts by weight: 100 parts of silicon carbide raw powder, 3-5 parts of sintering aid, 0.5-1.5 parts of polyvinyl alcohol, 0.5-1.5 parts of tetramethylammonium hydroxide, 0.5-1.5 parts of urea, and 0.5-1 part of release agent; the sintering aid is an aqueous dispersion containing yttrium oxide powder and aluminum oxide powder. This application reduces the possibility of surface overburning and internal underburning of ceramic products, improves the sintering success rate, and reduces the waste of silicon carbide raw powder.

[0004] For example, a high thermal conductivity pressureless sintered silicon carbide ceramic material with application number CN201510369366.0 and authorization announcement date 20190426 and a preparation method thereof are composed of the following raw materials in the following mass percentages: silicon carbide 75-95wt.%, graphene 0.5-10wt.%, surfactant 1-3wt.%, dispersant 0.5-2.5wt.%, binder 2-10wt.%, and boron carbide 0.5-3.5wt.%. The present invention uses a specific ratio between silicon carbide, graphene, and boron carbide, presses them into a green body, and sinters them pressurelessly under vacuum conditions to obtain SiC ceramic material. The graphene is evenly distributed in the SiC matrix material and forms a tight bond with the SiC, avoiding the reduction in thermal conductivity caused by phonon scattering by the internal pores of the material, which offsets and exceeds the effect of introducing graphene on improving thermal conductivity. This ensures the densification of the ceramic material while achieving a higher thermal conductivity and ensuring the uniformity of the material.

[0005] The above-mentioned and existing methods for preparing pressureless sintered silicon carbide ceramics are difficult to accurately predict and control sintering shrinkage and deformation for complex multi-cavity special-shaped cross-section components, which can easily lead to insufficient dimensional accuracy and internal stress concentration. In terms of improving material density, toughness and surface hardness, especially in ensuring the uniformity of the overall performance of complex-shaped components, the existing methods have limited effects or complex processes, and there are insufficient effective strengthening measures for stress concentration areas such as the corners of special-shaped beams. It is difficult to evenly form a deep and dense protective layer with high hardness and high bonding strength on the complex surface, and the stability of the overall performance of the component is insufficient. Summary of the Invention

[0006] The object of the present invention is to provide a pressureless sintered silicon carbide ceramic special-shaped beam and a preparation method thereof, so as to solve the above-mentioned deficiencies in the prior art.

[0007] In order to achieve the above object, the present invention provides the following technical solutions: A pressureless sintered silicon carbide ceramic special-shaped beam includes the following components and structures: Material composition: The matrix material is silicon carbide powder: the particle size is bimodal, with the main phase being 3-5μm and the nanophase being 0.5-1μm; Composite sintering aid: It is composed of Al2O3, Y2O3, MgO and CeO2 in a mass ratio of 4:3:1:1. The total addition amount is 3-5% of the mass of the base material. The molar ratio of Al2O3 to Y2O3 in the composite sintering aid is 1:0.58, and the molar ratio of MgO to CeO2 is 1:1; Reinforcement phase: Graphene and Ti3SiC2 are used. The total amount of graphene added is 0.5-2% of the mass of the matrix material. Graphene has a lamellar structure with a single layer thickness of ≤5nm and a lateral size of 1-5μm. The surface is hydroxylated and evenly dispersed in the matrix. The total amount of Ti3SiC2 added is 5-15% of the mass of the matrix material. The surface of the special-shaped beam is siliconized to form a dense layer with a thickness of 10-30 μm and a surface hardness of ≥2800 HV. The silicon source of the siliconization treatment is a polycarbosilane precursor, the treatment temperature is 1600-1700° C., and the siliconization time is 2-4 hours. The cross section of the special-shaped beam is a multi-cavity special-shaped structure with the number of sides being ≥4.

[0008] A method for preparing a pressureless sintered silicon carbide ceramic special-shaped beam comprises the following steps: Step 1. Data Collection and Modeling: Collect previous special-shaped beam preparation data and expert analysis data to build a 3D virtual model of the special-shaped beam. By collecting real-time slurry viscosity, injection molding pressure, and temperature data, the 3D virtual model is input to simulate sintering shrinkage and stress distribution, predict shrinkage, dynamically adjust mold size, optimize powder grading, and predict the optimal sintering curve. The 3D virtual model of special-shaped beams integrates the sintering dynamics model and the LSTM algorithm shrinkage model; The 3D virtual model of the special-shaped beam predicts the grain growth rate in real time (error ≤ 8%) and simultaneously optimizes the coarse / medium / fine particle grading ratio to (3.5-4.5): (2.5-3.5): (2.5-3.5). It then predicts the shrinkage rate and dynamically adjusts the mold size (compensation amount 0.5-1.2%).

[0009] Step 2. Material preparation and green body preparation: (1) Silicon carbide powder, composite sintering aid and graphene are mixed in proportion and ball milled for 24-48 hours to obtain a slurry. The slurry is then allowed to stand in a constant temperature and humidity environment for a period of time to form a uniform mud. After the ball milling, the slurry viscosity is controlled at 3000-5000 mPa·s and the solid content is ≥55 vol%. When the slurry is kept at a constant temperature and humidity: the temperature is 20-30 ° C, the humidity is 50-70%, and the time is 5-7 days.

[0010] (2) The obtained uniform mud material is dispersed in an acrylamide system with a pH of 10-11, injected into a gypsum mold for molding, and allowed to stand to obtain a molded body; (3) The green body is then impregnated with a tung oil-glutinous rice paste composite liquid with a mass ratio of 1:2 and dried at low temperature to form a pre-reinforced network; a six-immersion and six-drying process is adopted during the impregnation, and the impregnated tung oil-glutinous rice paste composite liquid is also added with a nano-silica sol with a particle size of 20-50nm and a mass fraction of 5-10%. After impregnation, it is exposed to sunlight or dried at 60℃ to form a three-dimensional organic-inorganic composite network, and the green body's flexural strength is increased by more than 30%.

[0011] Step 3. Pressureless step sintering: The green body obtained in the above step is fed into a sintering furnace. Before sintering, the green body surface is micro-hammered with an energy density of 0.5-1.2 J / mm² to induce grain orientation and increase the fracture toughness at the corners to 7.2 MPa·m¹ / ². The sintering furnace is then started for sintering. The sintering process is divided into three stages, as shown below: Degreasing stage: heating to 800℃ at 2-3℃ / min and keeping warm for 1.5-2h; Pre-sintering stage: heating to 1400℃ at 5℃ / min, keeping warm for 0.4-0.6h, then heating to 1600℃ at 3℃ / min, keeping warm for 0.8-1h; Final sintering stage: heating to 2050-2150℃ at 8℃ / min and keeping warm for 2-4h; During the sintering process, the temperature / shrinkage data is fed back through an embedded fiber optic sensor (the monitoring frequency of the selected embedded fiber optic sensor is ≥10Hz, and the gradient of the heating rate change during dynamic parameter adjustment is ≤2°C / min). The data is then input into the 3D virtual model of the special-shaped beam to predict the deformation and stress distribution, and the sintering parameters are dynamically adjusted. If the predicted deformation is greater than 0.5%, the heating rate is automatically reduced to 4°C / min. Step 4. Post-processing and verification: After sintering, the obtained sample is sent to the hot isostatic pressing equipment and then held under argon for a period of time. During hot isostatic pressing, the temperature and pressure are adjusted (the SiCl4 vapor partial pressure is controlled at 0.3-0.5MPa during the initial siliconization treatment, and the thickness of the β-SiC nanocrystalline layer generated by the reaction is negatively correlated with the porosity (R²≥0.92)). SiCl4 vapor is introduced into the beam under high temperature to react and form a β-SiC nanocrystalline layer for the initial siliconization. After the holding period, a polycarbosilane precursor is coated on the surface of the beam and siliconized at high temperature in a vacuum furnace for a period of time for the secondary siliconization (the temperature of the secondary siliconization is 1600-1700℃ and the time is 2-4h). After the siliconization is completed, the beam is sent to the reduction furnace and treated under high temperature to form an Fe3O4 protective film. During the reduction, the Fe 3+ / Fe 2+ The ratio is (1.8-2.2), and the Fe(CO)5 flow rate is dynamically adjusted. During the formation of the Fe3O4 protective film, the Fe(CO)5 vapor flow rate and the temperature gradient satisfy ΔQ=0.0005T²-0.12T+0.8 (T is the temperature in °C; ΔQ is in L / min), and the film thickness is controlled at 2-5μm. Laser microtexturing treatment is added to form staggered microgrooves with a depth of 50-100μm and a width of 20-30μm on the surface, extending the crack propagation path by 300%. The final product is obtained and verified by thermal shock cycles of more than 50 times at 1500-2000°C.

[0012] In the above technical solution, the present invention provides a pressureless sintered silicon carbide ceramic special-shaped beam and a preparation method thereof, which has the following beneficial effects: (1) The present invention achieves multi-scale synergistic strengthening and surface gradient protection through innovative design of material composition and structure. The matrix adopts bimodal distribution of silicon carbide powder. The synergistic effect of micron-sized particle skeleton and nanoparticle filling pores can significantly reduce the internal cracks of irregular cross-sections caused by uneven shrinkage. At the same time, the composite sintering aid can inhibit the abnormal growth of grains, synergistically reduce the sintering temperature, and reduce the deformation risk of multi-cavity structures. The gradient reinforcement phase greatly improves the crack propagation resistance of edges and corners, and solves the problem of uneven hardening layer at irregular edges and corners through deep silicon infiltration strengthening.

[0013] (2) The present invention realizes the real-time prediction of the shrinkage rate and stress distribution of special-shaped beams by integrating the sintering dynamics model and the LSTM algorithm into a three-dimensional virtual modeling system. In addition, the bimodal distribution of silicon carbide powder and dynamic particle grading optimization are combined to improve the accuracy of mold size compensation, significantly improve the dimensional accuracy of complex multi-cavity structures, and effectively suppress sintering deformation.

[0014] (3) The present invention uses micro-hammering on the surface of the blank to induce directional grain arrangement, combined with a six-immersion and six-drying process to form a three-dimensional organic-inorganic composite network, which improves the fracture toughness at the edges and corners. Subsequent laser micro-texturing forms 50-100 μm deep staggered micro-grooves on the surface, extending the crack propagation path by 300%, effectively solving the brittle fracture problem in the stress concentration area of ​​the special-shaped parts. At the same time, the wear resistance and erosion resistance of the complex curved surface are greatly improved through the synergistic effect of hot isostatic pressing and two-time siliconization.

[0015] (4) The present invention overcomes the four major technical bottlenecks of dimensional accuracy, stress concentration, brittle edges and surface strengthening of special-shaped beams through the synergistic effects of bimodal powder + multiphase reinforcement material design, gradient siliconization + green body pretreatment process innovation, and LSTM model + real-time sensing intelligent control, significantly improving the structural stability and life in extreme environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments described in the present invention. For ordinary technicians in this field, other drawings can also be obtained based on these drawings.

[0017] Figure 1 This is a structural cross-sectional view of an embodiment of a pressureless sintered silicon carbide ceramic special-shaped beam and a preparation method thereof according to the present invention.

[0018] Figure 2 The present invention provides a schematic flow chart of a method for preparing a pressureless sintered silicon carbide ceramic special-shaped beam and a method thereof. DETAILED DESCRIPTION

[0019] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.

[0020] like Figure 1 As shown, an embodiment of the present invention provides a pressureless sintered silicon carbide ceramic special-shaped beam, including the following components and structures: Material composition: The matrix material is silicon carbide powder: the particle size is bimodal, with the main phase being 3-5μm and the nanophase being 0.5-1μm; Composite sintering aid: It is composed of Al2O3, Y2O3, MgO and CeO2 in a mass ratio of 4:3:1:1. The total addition amount is 3-5% of the mass of the base material. The molar ratio of Al2O3 to Y2O3 in the composite sintering aid is 1:0.58, and the molar ratio of MgO to CeO2 is 1:1; Reinforcement phase: Graphene (graphene surface hydroxylation modification to enhance its dispersion in the matrix) and Ti3SiC2 are selected. The total amount of graphene added is 0.5-2% of the matrix material mass. Graphene has a lamellar structure with a single layer thickness of ≤5nm and a lateral size of 1-5μm. The surface is hydroxylation-modified and evenly dispersed in the matrix. The total amount of Ti3SiC2 added is 5-15% of the matrix material mass. The surface of the special-shaped beam is siliconized to form a dense layer with a thickness of 10-30 μm and a surface hardness of ≥2800 HV. The silicon source of the siliconization treatment is a polycarbosilane precursor, the treatment temperature is 1600-1700° C., and the siliconization time is 2-4 hours. The cross section of the special-shaped beam is a multi-cavity special-shaped structure with the number of sides being ≥4.

[0021] A method for preparing a pressureless sintered silicon carbide ceramic special-shaped beam, such as Figure 2 As shown, the following steps are included: Step 1. Data Collection and Modeling: Collect previous special-shaped beam preparation data and expert analysis data to build a 3D virtual model of the special-shaped beam (input parameters include powder particle size distribution, sintering aid melting point, and graphene thermal conductivity). Real-time data on slurry viscosity, injection molding pressure, and temperature are collected and input into the 3D virtual model to simulate sintering shrinkage and stress distribution, predict shrinkage, dynamically adjust mold size, optimize powder grading, and predict the optimal sintering curve. The 3D virtual model of special-shaped beams integrates the sintering dynamics model and the LSTM algorithm shrinkage model; The 3D virtual model of the special-shaped beam predicts the grain growth rate in real time (error ≤ 8%) and simultaneously optimizes the coarse / medium / fine particle grading ratio to (3.5-4.5): (2.5-3.5): (2.5-3.5). It then predicts the shrinkage rate and dynamically adjusts the mold size (compensation amount 0.5-1.2%).

[0022] Step 2. Material preparation and green body preparation: (1) Silicon carbide powder, composite sintering aid and graphene are mixed in proportion and ball milled for 24-48 hours to obtain a slurry. The slurry is then allowed to stand in a constant temperature and humidity environment for a period of time to form a uniform mud. After the ball milling, the slurry viscosity is controlled at 3000-5000 mPa·s and the solid content is ≥55 vol%. The slurry is kept at a constant temperature and humidity for 6 days: temperature 25°C, humidity 60%.

[0023] (2) The obtained uniform mud material is dispersed in an acrylamide system with a pH of 10-11, injected into a gypsum mold for molding, and allowed to stand to obtain a molded body; (3) The green body is then impregnated with a tung oil-glutinous rice paste composite liquid with a mass ratio of 1:2 and dried at low temperature to form a pre-reinforced network; a six-immersion and six-drying process is adopted during the impregnation, and the impregnated tung oil-glutinous rice paste composite liquid is also added with a nano-silica sol with a particle size of 20-50nm and a mass fraction of 5-10%. After impregnation, it is exposed to sunlight or dried at 60℃ to form a three-dimensional organic-inorganic composite network, and the green body's flexural strength is increased by more than 30%.

[0024] Step 3. Pressureless step sintering: The green body obtained in the above step is fed into a sintering furnace. Before sintering, the green body surface is micro-hammered with an energy density of 0.5-1.2 J / mm² to induce grain orientation and increase the fracture toughness at the corners to 7.2 MPa·m¹ / ². The sintering furnace is then started for sintering. The sintering process is divided into three stages, as shown below: Degreasing stage: heating to 800℃ at 2-3℃ / min and keeping warm for 1.5-2h; Pre-sintering stage: heating to 1400℃ at 5℃ / min, keeping warm for 0.4-0.6h, then heating to 1600℃ at 3℃ / min, keeping warm for 0.8-1h; Final sintering stage: heating to 2050-2150℃ at 8℃ / min and keeping warm for 2-4h; During the sintering process, the temperature / shrinkage data is fed back through an embedded fiber optic sensor (the monitoring frequency of the selected embedded fiber optic sensor is ≥10Hz, and the gradient of the heating rate change during dynamic parameter adjustment is ≤2°C / min). The data is then input into the 3D virtual model of the special-shaped beam to predict the deformation and stress distribution, and the sintering parameters are dynamically adjusted. If the predicted deformation is greater than 0.5%, the heating rate is automatically reduced to 4°C / min. Step 4. Post-processing and verification: After sintering, the obtained sample is sent to the hot isostatic pressing equipment and then held in an argon environment for a period of time. During hot isostatic pressing, the temperature is 1800℃, the pressure is 150MPa, the holding time is 1h, and the heating and cooling rate of the hot isostatic pressing treatment is 10℃ / min; and during holding, the temperature and pressure are adjusted (the SiCl4 vapor partial pressure is controlled at 0.3-0.5MPa during the initial siliconization treatment, and the thickness of the β-SiC nanocrystalline layer generated by the reaction is negatively correlated with the porosity (R²≥0.92)). SiCl4 vapor is introduced into the beam under high temperature to react and form a β-SiC nanocrystalline layer for the initial siliconization. After the holding is completed, a polycarbosilane precursor is coated on the surface of the beam, and siliconized at high temperature for a period of time in a vacuum furnace for a secondary siliconization (the temperature of the secondary siliconization is 1600-1700℃ and the time is 2-4h). After the siliconization is completed, it is sent to the reduction furnace and treated in a high temperature environment to form an Fe3O4 protective film. During the reduction, the Fe 3+ / Fe 2+ The ratio is (1.8-2.2), and the Fe(CO)5 flow rate is dynamically adjusted. During the formation of the Fe3O4 protective film, the Fe(CO)5 vapor flow rate and the temperature gradient satisfy ΔQ=0.0005T²-0.12T+0.8 (T is the temperature in °C; ΔQ is in L / min), and the film thickness is controlled at 2-5μm. Laser microtexturing treatment is added to form staggered microgrooves with a depth of 50-100μm and a width of 20-30μm on the surface, extending the crack propagation path by 300%. The final product is obtained and verified by thermal shock cycles of more than 50 times at 1500-2000°C.

[0025] Example (this application solution) Raw material ratio: SiC powder: bimodal distribution (main phase 4μm accounts for 70wt%, nanophase 0.8μm accounts for 30wt%); Sintering aid: Al2O3 / Y2O3 / MgO / CeO2=4:3:1:1 (total addition amount 4wt%); Reinforcement phase: hydroxylated graphene (1.5wt%) + Ti3SiC2 (10wt%).

[0026] Preparation method: 1. Digital Modeling: Input 12 parameters including powder D50 = 3.8 μm, graphene thermal conductivity 5300 W / (m·K); Dynamic compensation mold size: shrinkage rate prediction value 1.05% (actual measurement 1.08%, error 0.03%).

[0027] 2. Traditional method of soaking: Tung oil-glutinous rice paste composite liquid (1:2) + 8wt% nano-silica sol; Six-immersion and six-drying cycle parameters: ;

[0028] The open porosity of the green body was reduced to 4.7%.

[0029] 3. Sintering control: Micro hammer energy: 0.8J / mm 2 (KIC at corners = 7.3MPa·m 1 / 2 ); Fiber optic sensor feedback: Predicted deformation at 1600°C: 0.52% → Automatically reduce speed to 4°C / min.

[0030] 4. Surface treatment: Initial siliconization: SiCl4 partial pressure 0.45MPa (thickness 28μm, HV=2980); Secondary siliconization: PCS precursor viscosity 180 cP (thickness deviation ± 1.5 μm); Blueing process: Fe(CO)5 flow Q=0.05×890 2 -1.2×890+8=35.2mL / min→Fe3O4 film thickness 3.8μm.

[0031] Verification results: ;

[0032] Comparative Example 1 (without ancient method of soaking) 1. Changes: Delete the tung oil-glutinous rice paste impregnation and six-impregnation and six-drying processes; The green body is directly dried and then sintered; 2. Performance comparison: Open porosity: 9.8% (108% higher than Example 1); Flexural strength: 521 MPa (↓22%) Thermal shock cycle failure: 32 times (↓45%).

[0033] Comparative Example 2 (No Digital Twin Control) 1. Changes: A fixed sintering curve (5°C / min to 2050°C) was used; Eliminate fiber optic sensors and dynamic parameter adjustment; 2. Performance comparison: Crack density at corners: 15 cracks / cm (3 cracks / cm in Example 1); Size deviation: +1.85% (0.65pt beyond the compensation range); Final sintering deformation: 1.2% (triggering automatic shutdown).

[0034] Comparative Example 3 (Single Siliconizing Treatment) 1. Changes: Cancel SiCl4 vapor phase siliconization and only retain PCS liquid phase siliconization; The blueing process does not add MgAl2O4 multiphase strengthening; ‌Performance Comparison‌: ;

[0035] 2. Mechanism Analysis: The organic-inorganic network formed by six-impregnation and six-drying processes significantly reduces the green body porosity, and in conjunction with the real-time deformation correction of the digital twin, uniformizes the sintering stress distribution. The double composite siliconized layer, through the interlaced structure of β-SiC nanocrystals (gas phase) and SiC whiskers (liquid phase), blocks the crack propagation path by 300%.

[0036] The above description is merely illustrative of certain exemplary embodiments of the present invention. It goes without saying that those skilled in the art will be able to modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the above drawings and description are illustrative in nature and should not be construed as limiting the scope of protection of the claims.

Claims

1. A pressureless sintered silicon carbide ceramic special-shaped beam, characterized in that: It includes the following components and structures: Material composition: The matrix material is silicon carbide powder: the particle size is bimodal, with the main phase being 3-5 μm and the nanophase being 0.5-1 μm; Composite sintering aid: It is composed of Al2O3, Y2O3, MgO and CeO2 in a mass ratio of 4:3:1:

1. The total addition amount is 3-5% of the mass of the base material. The molar ratio of Al2O3 to Y2O3 in the composite sintering aid is 1:0.58, and the molar ratio of MgO to CeO2 is 1:1; Reinforcement phase: Graphene and Ti3SiC2 are used. The total amount of graphene added is 0.5-2% of the mass of the matrix material. Graphene has a lamellar structure with a single layer thickness of ≤5nm and a lateral size of 1-5μm. The surface is hydroxylated and evenly dispersed in the matrix. The total amount of Ti3SiC2 added is 5-15% of the mass of the matrix material. The surface of the special-shaped beam is siliconized to form a dense layer with a thickness of 10-30 μm and a surface hardness of ≥2800 HV. The silicon source of the siliconization treatment is a polycarbosilane precursor, the treatment temperature is 1600-1700° C., and the siliconization time is 2-4 hours. The cross section of the special-shaped beam is a multi-cavity special-shaped structure with the number of sides being ≥4.

2. The method for preparing a pressureless sintered silicon carbide ceramic special-shaped beam according to claim 1, characterized in that: The following steps are involved: Step 1. Data Collection and Modeling: Collect previous special-shaped beam preparation data and expert analysis data to build a 3D virtual model of the special-shaped beam. By collecting real-time slurry viscosity, injection molding pressure, and temperature data, the 3D virtual model is input to simulate sintering shrinkage and stress distribution, predict shrinkage, dynamically adjust mold size, optimize powder grading, and predict the optimal sintering curve. Step 2. Material preparation and green body preparation: (1) Silicon carbide powder, composite sintering aid and graphene are mixed in proportion and ball milled for 24-48 hours to obtain a slurry. The slurry is then placed in a constant temperature and humidity environment for a period of time to form a uniform slurry; (2) The obtained uniform mud material is dispersed in an acrylamide system with a pH of 10-11, injected into a gypsum mold for molding, and allowed to stand to obtain a molded body; (3) The green body is then impregnated with a tung oil-glutinous rice paste composite liquid with a mass ratio of 1:2 and dried at low temperature to form a pre-reinforced network; Step 3. Pressureless step sintering: The green body obtained in the above step is fed into the sintering furnace, and then the sintering furnace is started for sintering. The process is divided into three stages, as shown below: (1) Degreasing stage: heating to 800℃ at 2-3℃ / min and keeping warm for 1.5-2h; (2) Pre-sintering stage: heating to 1400°C at 5°C / min, keeping warm for 0.4-0.6h, then heating to 1600°C at 3°C / min, keeping warm for 0.8-1h; (3) Final sintering stage: heating to 2050-2150℃ at 8℃ / min and keeping warm for 2-4h; During the sintering process, embedded fiber optic sensors provide feedback on temperature and shrinkage data, which are then fed into a 3D virtual model of the special-shaped beam to predict deformation and stress distribution, allowing for dynamic adjustment of sintering parameters. Step 4. Post-processing and verification: After sintering, the obtained sample is sent to the hot isostatic pressing equipment, and then the pressure is maintained for a period of time in an argon environment. During the pressure maintenance, the temperature and pressure are adjusted, and SiCl4 vapor is introduced into the high temperature environment to react to form a β-SiC nanocrystalline layer for the first siliconization. After the pressure maintenance is completed, the polycarbosilane precursor is coated on the surface of the beam, and the sample is siliconized at high temperature in a vacuum furnace for a period of time for the second siliconization. After the siliconization is completed, it is sent to a reduction furnace and treated in a high temperature environment to form an Fe3O4 protective film to obtain the final product. The final product is verified by thermal shock cycles of more than 50 times at 1500-2000℃.

3. The pressureless sintered silicon carbide ceramic special-shaped beam and the preparation method thereof according to claim 2, characterized in that: In step 1: The 3D virtual model of special-shaped beams integrates the sintering dynamics model and the LSTM algorithm shrinkage model; The 3D virtual model of the special-shaped beam predicts the grain growth rate in real time (error ≤ 8%) and simultaneously optimizes the coarse / medium / fine particle grading ratio to (3.5-4.5): (2.5-3.5): (2.5-3.5). It then predicts the shrinkage rate and dynamically adjusts the mold size (compensation amount 0.5-1.2%).

4. The pressureless sintered silicon carbide ceramic special-shaped beam and the preparation method thereof according to claim 2, characterized in that: In step 2: After ball milling, the slurry viscosity is controlled at 3000-5000mPa·s and the solid content is ≥55vol%; The slurry is kept at constant temperature and humidity: temperature 20-30℃, humidity 50-70%, time 5-7 days.

5. The pressureless sintered silicon carbide ceramic special-shaped beam and the preparation method thereof according to claim 2, characterized in that: In step 2: During the impregnation process, a six-impregnation and six-drying process is adopted. The tung oil-glutinous rice paste composite liquid for impregnation also needs to be added with nano-silica sol with a particle size of 20-50nm and a mass fraction of 5-10%. After impregnation, it is exposed to sunlight or dried at 60℃ to form a three-dimensional organic-inorganic composite network, and the bending strength of the green body is increased by more than 30%.

6. The pressureless sintered silicon carbide ceramic special-shaped beam and the preparation method thereof according to claim 2, characterized in that: In step 3: Before sintering, the green body surface is micro-hammered with an energy density of 0.5-1.2J / mm² to induce grain orientation and increase the fracture toughness at the corners to 7.2MPa·m¹ / ²; The monitoring frequency of the selected embedded optical fiber sensor is ≥10Hz, and the gradient of the heating rate change is ≤2℃ / min when the parameters are dynamically adjusted.

7. The pressureless sintered silicon carbide ceramic special-shaped beam and the preparation method thereof according to claim 2, characterized in that: In step 3: If the predicted deformation is greater than 0.5%, the heating rate will be automatically reduced to 4°C / min.

8. The pressureless sintered silicon carbide ceramic special-shaped beam and the preparation method thereof according to claim 2, characterized in that: In step 4: Hot isostatic pressing: temperature 1600-2000℃, pressure 140-160MPa, holding time 0.8-1.2h; During the initial siliconizing treatment, the SiCl4 vapor partial pressure was controlled at 0.3-0.5 MPa, and the thickness of the β-SiC nanocrystalline layer generated by the reaction was negatively correlated with the porosity (R²≥0.92).

9. The pressureless sintered silicon carbide ceramic special-shaped beam and the preparation method thereof according to claim 2, characterized in that: In the step S4: The temperature during secondary siliconizing is 1600-1700℃ and the time is 2-4h; During reduction, Fe 3+ / Fe 2+ The ratio is (1.8-2.2), and the Fe (CO) 5 flow rate is dynamically adjusted. During the formation of the Fe3O4 protective film, the Fe (CO) 5 vapor flow rate and the temperature gradient satisfy ΔQ = 0.0005T² - 0.12T + 0.8 (T is temperature, unit ℃; ΔQ is L / min), and the film thickness is controlled at 2-5μm.

10. The pressureless sintered silicon carbide ceramic special-shaped beam and the preparation method thereof according to claim 2, characterized in that: In step 4: Adding laser micro-texturing treatment, staggered micro-grooves with a depth of 50-100 μm and a width of 20-30 μm are formed on the surface, extending the crack propagation path by 300%.

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